Jeremy,

The title makes more sense after reading the Wikipedia entry on
spherical cows.

Nick.

On 22/09/2021 14:24, Jeremy Shears wrote:
>
> This ApJ submission on ArXiv certainly has an eye-catching title: https://arxiv.org/abs/2109.09852<https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Farxiv.org%2Fabs%2F2109.09852&data=04%7C01%7C%7C8760c18887dc4ec10a1c08d97dcb17fc%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637679133499073833%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=qcCtlZtSOLCa7XICihaF8HlJm1V3hRpdsuc9%2BGKmYoE%3D&reserved=0>
>
> C/2014 UN271 (Bernardinelli-Bernstein): the nearly spherical cow of comets
>
> Pedro H. Bernardinelli, Gary M. Bernstein, Benjamin T. Montet, Robert Weryk, Richard Wainscoat, M. Aguena, S. Allam, F. Andrade-Oliveira, J. Annis, S. Avila, E. Bertin, D. Brooks, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, R. Cawthon, C. Conselice, M. Costanzi, L. N. da Costa, M. E. S. Pereira, J. De Vicente, H. T. Diehl, S. Everett, I. Ferrero, B. Flaugher, J. Frieman, J. García-Bellido, E. Gaztanaga, D. W. Gerdes, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, S. R. Hinton, D. L. Hollowood, K. Honscheid, D. J. James, K. Kuehn, N. Kuropatkin, O. Lahav, M. A. G. Maia, J. L. Marshall, F. Menanteau, R. Miquel, R. Morgan, R. L. C. Ogando, F. Paz-Chinchón, A. Pieres, A. A. Plazas Malagón, M. Rodriguez-Monroy, A. K. Romer, A. Roodman, E. Sanchez, M. Schubnell, S. Serrano, I. Sevilla-Noarbe, M. Smith, M. Soares-Santos, E. Suchyta, M. E. C. Swanson, G. Tarle, C. To, M. A. Troxel, T. N. Varga, A. R. Walker, Y. Zhang (for the DES Collaboration)
>
> C/2014 UN271 (Bernardinelli-Bernstein) is a comet incoming from the Oort cloud which is remarkable in having the brightest (and presumably largest) nucleus of any well-measured comet, and having been discovered at heliocentric distance rh≈29 au farther than any Oort-cloud member. We describe the properties that can be inferred from images recorded until the first reports of activity in June 2021. The orbit has i=95∘, with perihelion of 10.97 au to be reached in 2031, and previous aphelion at 40,400±260 au. Backwards integration of the orbit under a standard Galactic tidal model and known stellar encounters suggests this is a pristine new comet, with a perihelion of q≈18 au on its previous perihelion passage 3.5 Myr ago. The photometric data show an unresolved nucleus with absolute magnitude Hr=8.0, colors that are typical of comet nuclei or Damocloids, and no secular trend as it traversed the range 34--23 au. For r-band geometric albedo pr, this implies a diameter of 150(pr/0.04)−0.5 km. There is strong evidence of brightness fluctuations at ±0.2 mag level, but no rotation period can be discerned. A coma consistent with a ``stationary' 1/ρ surface-brightness distribution grew in scattering cross-section at an exponential rate from Afρ≈1 m to ≈150 m as the comet approached from 28 to 20 au. The activity is consistent with a simple model of sublimation of a surface species in radiative equilibrium with the Sun. The inferred enthalpy of sublimation matches those of CO2 and NH3. More-volatile species -- N2, CH4, and CO -- must be far less abundant on the sublimating surfaces.
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